1. Field of the Invention
The present invention relates to a CMOS solid state image sensor, and an image sensing apparatus incorporated with the solid state image sensor.
2. Description of the Related Art
Conventionally, there is known a document reading device provided with a CMOS image sensor, wherein plural pixel arrays for receiving light of R (red), G (green), and B (blue) i.e. plural one-dimensional pixel arrays are arranged in rows. In the document reading device, a scanning operation is performed by mechanically moving a CMOS image sensor, an imaging optics, or a document. In performing the scanning operation, if an operation error such as feeding displacement occurs, each of the pixel arrays may read an image at a displaced position, with the result that serious color displacement may be generated in a reproduced image. In view of this, for instance, JP 2007-336519A (D1) proposes a CMOS image sensor of a simplified arrangement, wherein the pitch between one-dimensional pixel arrays is reduced, to suppress color displacement in a reproduced image resulting from generation of feeding displacement by a scanning operation.
The conventional CMOS image sensor recited in D1 is provided with a pixel circuit including a light receiving element, a transfer transistor, a reset transistor, a floating diffusion (FD), an amplification transistor, and a row selecting transistor in each of the pixels. In this arrangement, since a large area is used for the pixel circuits provided in the pixels, if an area of openings for receiving light by the light receiving elements is increased, the area of the pixels may be increased. In the CMOS image sensor, for instance, in the case where adjacent pixel arrays are arranged in proximity to each other, if the area of each pixel is increased, the pitch between the pixel arrays is also increased, because the size of a pixel corresponds to a pitch between pixel arrays. Thus, as described above, the size of a pixel is reduced by a decrease in the pitch between pixel arrays, with the result that the area of the openings for receiving light is also reduced. As a result, it is impossible to receive sufficient amount of light, and the sensitivity of the CMOS image sensor may be deteriorated.
In view of the above, there is known a CMOS image sensor provided with plural rows of pixel arrays adapted to receive light of a corresponding color component (spectral characteristic) with respect to an object, and adapted to perform a TDI (Time Delay Integration) operation. The TDI operation is a readout operation with respect to an identical frame, while time-wise shifting the pixel arrays row by row. The solid state image sensor having the above arrangement has a drawback that it is sometimes impossible to properly remove a reset noise of a floating diffusion included in a signal to be obtained by the readout operation.